The story revolves around Tomoya Mizuhara, a 13-year-old boy who suddenly gains a big sister when his father remarries. 17-year-old Ichika is a little strange, and her affection for Tomoya is rather overwhelming, if not scary
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Big Sister Research, and that means coming to school. And turning Fujisaki against Tomoya. Sorry for not being cute enough, I guess. Pretty amusing episode here seeing how Ichika causes quite the stir showing up at school.

Tomoya, meet Ichika's friends, a busty gal and one who is into wrestling. And what does Tomoya do? Go over to Mitsuru's house to seek refuge. And what does Mitsuru do? Go out and get to know Ichika's friends personally. This episode is pretty fun given its length.

I have actually experienced something similar to this anime. Granted there were no yanderes. When I was really young, like 8 or 9, I had a few female relatives in their late teens who loved to cuddle me. The only feelings I remember were of embarrassment and wanting to escape to play SNES with my male relatives. Now that I am a grown man I must admit I am jealous of Tomoya's situation, but I know that put in the same situation, I would probably take a similar course of action to his.